California Agriculture

Foliar spraying was found to be an effective method to rapidly increase boron levels in most vegetative and reproductive tissues in grapevines. The reduction of fruit-set deficiency symptoms with a pre-bloom or bloom spray was immediate but not complete. Foliar sprays applied during the previous fall were more effective in reducing such symptoms than pre-bloom or bloom sprays. This may be due to the earlier incorporation of boron in reproductive tissues, especially dormant buds. Grapevine foliage is also more tolerant to boron postharvest in the fall, when 1 pound per acre of actual boron can be safely applied. Spring and summer sprays of boron should be limited to 1/2 pound per acre per application to avoid phytotoxicity.